查看更多>>摘要：Abstract The Pacific Lamprey Entosphenus tridentatus is an important species both ecologically and culturally, but their population numbers and range have declined severely in the past several decades in the Columbia Basin. In freshwater ecosystems, larval lampreys are candidate prey species for many fish predators, but little is known regarding the magnitude of predation they currently experience. Predation on larval Pacific Lampreys may be substantially underestimated by morphological gut content analysis because their soft bodies are quickly digested and leave no hard evidence, such as bones and scales. We conducted an experimental predation study and analyzed larval Pacific Lampreys in the gut contents of predators’ digestive tracts via both morphological and molecular methods. Whereas most consumed larval lampreys (67–100%) were morphologically unidentifiable within two nights, genetic species identification rates using four single nucleotide polymorphisms from stomachs were high (83%). The single nucleotide polymorphisms optimized for parentage in Pacific Lamprey also successfully identified the parents of four out of five Pacific Lampreys with complete genotypes. When a genetic baseline of candidate parents is available, this molecular technique using parentage‐based tagging offers a novel method for determining precise characteristics of predation behavior in field studies, including the ages and natal origins of larvae being consumed.
查看更多>>摘要：Abstract Fishery managers have struggled for decades to rebuild stocks of Atlantic Cod Gadus morhua in the northwestern Atlantic Ocean, and the resolution of current fine‐scale population structure will surely help those efforts. Using double digest restriction‐site associated DNA sequencing, we analyzed 248 adult and 215 juvenile Atlantic Cod collected from areas bordering the Canada–USA boundary in 2017–2018. Chromosomal inversions from linkage group (LG) 2 and LG 7 contribute the largest amount of variance to the data set. A southwesterly decrease in the proportion of LG 1 inversion haplotypes may indicate gene flow from areas north of 45°N. Samples from both the northern Gulf of Maine and Bay of Fundy were genetically distinct from all other samples, suggesting that local spawning groups may still be active. Genetic similarities between Atlantic Cod from Browns Bank and eastern Georges Bank indicate that transborder gene flow is ongoing. These results will help to better define the stocks in order to guide the implementation of management strategies in the USA and Canada, which should consider rebuilding exhausted and genetically isolated populations.
Stephen WinsorSteve BlumenshinePaul AdeliziMatt Bigelow...
15页
查看更多>>摘要：Abstract Salmonid populations of the Central Valley of California have been in decline for decades, making hatchery practices that combine conservation strategies with targeted research essential to optimize recruitment to adulthood. Hatchery populations generally exhibit a higher incidence of precocious male maturation than natural populations. However, optimal hatchery management practices pertaining to incubation, feeding, and genetic predisposition have yet to be optimized to lower the incidence of precocity in hatchery‐reared male spring‐run Chinook Salmon Oncorhynchus tshawytscha. To further assess this, we conducted a 2?×?2 factorial experiment exploring the effect of embryo incubation temperature (cold or warm) and post‐ponding ration (high or low) on incidence of age‐1 precocious male maturation. Fertilized eggs from each parental cross were placed among each treatment group to control for genetic variation and track any genetic predisposition. Precocity rate at year 1 was affected by incubation temperature and feed rate. There were also significant differences in growth rate and body condition among the treatment groups during early development. Additionally, the precocious males were nonrandomly produced by the crosses, suggesting a significant parentage effect on precocity. Optimization of Chinook Salmon rearing techniques is critical—not only to lessen the incidence of precocity and identify the causal parameters, but also to maximize successful reintroduction.
查看更多>>摘要：Abstract The body conductivity of fish (Cf; μS/cm) and the power density causing threshold immobilization (Dm; μW/cm3) play a critical role in determining electrofishing success. My aim was to compare two methods for estimating Cf and Dm: the response‐threshold method using live Rainbow Trout Oncorhynchus mykiss (12–15?cm TL) and the direct‐measure method using the carcasses of the same fish. The estimates were compared to values from other published studies. I also evaluated the effect of electric field constriction (e.g., depth effect) on Cf and Dm in tanks with water : fish cross‐sectional area ratios of 6:1, 25:1, and 100:1. The resulting data conformed to theory for both methods; that is, Cf and Dm increased with decreasing tank size because field constriction forced more electric current through a fish. Estimates of Cf and Dm by both methods were similar in the two larger tanks (25:1 and 100:1). I suggest a standard Cf value of 60 μS/cm for Rainbow Trout if they are the target species. This value is near the low end of a cluster of published values for various fishes (50–160?μS/cm) that are within cross‐sectional ratios of 20:1 to 100:1. A standard value for Dm cannot be recommended due to variation caused by electrical output and fish size and species. The direct‐measure method proved superior to the response‐threshold method because it requires fewer fish for estimates of Cf and Dm, does not depend on subjective determination of threshold in live fish, and provides information on water‐to‐fish power transfer efficiency.
Neil K. AshtonTyler J. RossRyan S. HardySarah M. Stephenson...
13页
查看更多>>摘要：Abstract Populations of Burbot Lota lota across the Holarctic ecozone are facing imperilment from environmental warming, particularly in ecosystems impacted by hydropower and climate change. We conducted a series of laboratory experiments to evaluate the tolerance of Burbot embryos to various thermal regimes. Both cyclical and constant warming between 4.0°C and 5.5°C during the initial 25 degree‐days of embryo development led to significant deformity and mortality of protolarvae, with faster rates of temperature increase (i.e., 0.4°C/d) causing greater harm than gradual rates of warming. Random family effects interacted with incubation temperature of embryos to account for significant variability in deformity and survival of protolarvae. These findings have management implications for identifying and/or augmenting the thermal fitness of populations in modified ecosystems, particularly in Burbot populations where aquaculture production supports abundance. A model of hatching time based on degree‐days of embryo development was also developed to improve predictions of natural emergence, peak larvae abundance, and optimal timing for larvae stocking. It is recommended that hydropower operations avoid thermopeaking during winter spawning of Burbot, especially if reservoir discharges exceed 4°C. Maintaining water temperatures below 3°C for at least the first 2?weeks of embryogenesis is critical for Burbot reproduction and underscores the importance of ice‐covered spawning habitats. Global climate trends are expected to exacerbate warming in rivers, and many challenges lie ahead for conservation efforts seeking to mitigate the risks of Burbot extirpation.
查看更多>>摘要：Abstract Larval Atlantic Croakers Micropogonias undulatus ingress into estuaries from offshore spawning sites during fall and winter. Larvae and early juveniles migrate up‐estuary to oligohaline nurseries where they reside for several months before emigrating seaward. We examined the ontogenetic changes in behavioral salinity preference and avoidance as potential contributors to these movement patterns along the estuarine salinity gradient. Four size‐classes (26–40, 41–55, 56–70, and 71–85?mm SL) were acclimated to 10‰ and 18°C and exposed to horizontal salinity gradients providing five discrete salinity choices: 2, 6, 10, 14, and 18‰. Behavioral salinity preference varied ontogenetically: 26–40‐mm juveniles avoided salinities ≤10‰ and preferred higher salinities, 41–55‐mm juveniles showed a shift toward lower salinities, and 56–70‐mm fish continued this trend by preferring 2‰ and avoiding 18‰. The largest fish tested (71–85?mm) showed no significant preference or avoidance behavior, although they tended to avoid the low and prefer the high salinities that were tested. The preference for higher salinities among early (26–40?mm) juveniles may facilitate orientation in higher‐salinity bottom waters by assisting up‐estuary immigration to oligohaline nurseries via the residual bottom‐layer inflow. The preference for low salinity of 56–70‐mm juveniles is consistent with their residence in oligohaline areas. We also conducted feeding and growth experiments, at 18°C, on 30–40‐mm and 75–85‐mm fish, corresponding to the smallest and largest fish in the salinity preference trials. Smaller juveniles showed no significant energetic advantage in oligohaline versus mesohaline conditions. However, larger juveniles grew significantly faster at 18‰ than at 2‰, indicating that down‐estuary movement during summer and fall improves growth capacity later in the nursery season. The increased precipitation and river discharge that is predicted from climate change and its associated stronger net up‐estuary flow of saline bottom waters may facilitate the up‐estuary immigration of early juvenile Atlantic Croakers through their attraction to higher salinity, as is demonstrated by the present work.
Jani HelminenAntóin M. O’SullivanTommi Linnansaari
10页
查看更多>>摘要：Abstract Imaging sonars, such as the Adaptive Resolution Imaging Sonar (ARIS), provide high‐resolution sonar data that are used in fisheries research and management. While sonar methods have enormous potential for making population estimates, species identification via sonar remains an unresolved challenge. One method that may overcome this challenge involves measuring tailbeat frequencies to guide species differentiation. The tailbeat frequencies of three commonly sympatric anadromous fish species of eastern North America, Atlantic Salmon Salmo salar, Striped Bass Morone saxatilis, and American Shad Alosa sapidissima, were measured from imaging sonar data collected in an experimental low‐flow, short‐range setup. The frequencies were significantly different between the species (mean ± 1 SD beats/s: 0.6?±?0.3 [Atlantic Salmon], 0.9?±?0.2 [Striped Bass], and 1.4?±?0.3 [American Shad]) when measured using a previously established manual method. Building on this, an automated method was developed and tested, and the method showed promising results. However, when compared to manually identified number of beats the error was large (on average, 1.1 [Atlantic Salmon], 4.8 [Striped Bass], and ?0.4 [American Shad] beats in a fish track), especially in high fish densities. Despite the limitations, the automated method has utility in fisheries management when high‐quality data can be collected for species with differing tailbeat frequencies.
Nicholas A. HerediaRobert E. GresswellMolly A. H. WebbTravis O. Brenden...
14页
查看更多>>摘要：Abstract In Yellowstone Lake, predation by invasive Lake Trout Salvelinus namaycush has caused significant abundance declines in native Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri. Lake Trout suppression has been ongoing since 1995; assessment and simulation modeling are used to measure suppression effectiveness and guide efforts. Lake Trout reproduction demographics are linked to these modeling efforts via quantification of the population stock–recruitment relationship. To improve estimation of this relationship for Lake Trout in Yellowstone Lake, we assessed reproduction demographics by quantifying spawning periodicity, size at maturity, and female fecundity. Histological assessment suggested that females with a gonadosomatic index (GSI) >3.0 and males with a GSI >1.0 were capable of spawning. Approximately 65% of mature females appeared to have spawned on an annual cycle. In 2015, the mean absolute and relative fecundities were 4,612 eggs and 1,535 eggs/kg, respectively; temporal differences in relative fecundity (1996, 2006, 2007, and 2015) were not statistically significant. Lake Trout population fecundity has declined from a peak in 2010 due to reduction in abundance of spawners. The estimated population fecundity of approximately 4.7 million eggs in 2020 represents an 81% decline from the mean estimate of previous samples and an 87% reduction from peak population fecundity. Despite declines in population fecundity, age‐2 recruitment has increased in recent years; our results suggest these increases are not related to changes in reproductive demographics, but rather are related to increased prerecruitment survival. Our results provide information for understanding temporal variation in spawning stock biomass of Lake Trout in Yellowstone Lake and the capacity of the population to respond to suppression. When responding to an invasive species, fishery managers should recognize that population characteristics (e.g., reproduction demographics, population dynamics) in invaded systems may differ from those in the species’ native range; such differences can influence the effectiveness of management actions and policies.
Brock M. HuntsmanAbigail J. LynchColleen A. Caldwell
14页
查看更多>>摘要：Abstract Density‐dependent (DD) and density‐independent (DI) effects play an important role in shaping fish growth rates, an attribute that correlates with many life history traits in fishes. Consequently, understanding the extent to which DD and DI effects influence growth rates is valuable for fisheries assessments because it can inform managers about how populations may respond as environmental conditions continue to change (e.g., threats from climate change). We used a Rio Grande Cutthroat Trout Oncorhynchus clarkii virginalis (RGCT) capture–mark–recapture data set collected over 2 years along a temperature and density gradient in northern New Mexico streams to test the extent to which DD and DI effects interact to influence specific growth rates. We found that temperature (DI) and density (DD) interacted with RGCT life stage (i.e., immature or mature) to affect growth rates. We only detected evidence of a negative DD effect on RGCT growth for the immature fraction of a population when exposed to the warmest stream temperatures. Our results suggest that competition most strongly affected the immature portion of RGCT populations, and this effect was only detectable when temperatures were warmest and energetic stress was likely at its highest. The quadratic relationship between temperature and growth rates also demonstrated that stream temperatures were below as well as above optimal growth temperatures for RGCT. Growth rates in our RGCT populations were influenced by complex interactions of DD and DI effects, and our results suggest that the negative consequences of warming trends associated with climate change on RGCT populations may be exacerbated by DD effects.
NSTL
Wiley